I think maybe it could be possible to use a Raspberry Pi and a photo diode to measure the frequencies of light sources. To hold the photo diode near to a incandescent bulb and then get the value 100 Hz or 120 Hz (depending on country).
It is probably very easy for an experienced GPIO user, but I don't know where to start. Do you think this is possible? I also would like to hold the diode near a computer monitor or smartphone and then see the light's flicker frequency which can be up to 10.000 Hz or even more.
Some PC monitor review sites test flicker rates. I wonder if it can be done with a Raspberry Pi.